1. Field of the Invention
The present invention relates to electronic circuits, and particularly to a current-mode analog computational circuit.
2. Description of the Related Art
The growing demand for portable operation of electronic systems and biomedical instruments has led to a trend of focusing on low-voltage and low-power designs. Current mode analog circuits are, therefore, very attractive candidates for portable applications where low power consumption and long battery life are key factors. This is because in current-mode circuits, the input and output signals are currents. Furthermore, the circuit performance is determined by currents and the voltage levels are generally irrelevant in determining the circuit performance. Typically, the nodes inside current mode circuits are low-impedance nodes. Thus, the voltage swings are usually small and, therefore, operation from low-voltage supplies is feasible. With low impedance nodes, the time constant of the circuits is relatively low and this results in wide bandwidth circuits. Moreover, in current-mode, the circuits' high gain is, in large part, not required. This results in simpler hardware structures and justifies the growing range of applications of the current-mode circuits, such as in neural networks, microwave and optical systems, continuous time filters and sampled data filters.
A conventional analog multiplier has been widely used as a basic building block in many analog signal processing applications, such as modulators, equalizers, frequency doublers and neural network applications. Existing methods to realize low power consumption in the circuit include using MOSFETs working in weak inversion.
One typical multiplier is a voltage-mode multiplier, with input voltages and an output voltage. This typical multiplier is usually very sensitive to temperature variations. Another typical circuit is a current-mode based circuit that utilizes conventional differential techniques. A major disadvantage of these current-mode based circuits is usually a requirement for a relatively large number of current sources. Another major disadvantage, for example, is a requirement for relatively large aspect ratios for most of the transistors. Consequently, these requirements can increase the cost of the circuit, and can increase power dissipation and degrade the bandwidth of the circuit.
Alternative designs for a four-quadrant multiplier circuit typically are not current-mode based. These alternative design four-quadrant multiplier circuits are usually transresistance based with the output voltage proportional to the multiplication of the input currents. Others alternative design four-quadrant multiplier circuits are usually transconductance based where the output currents are proportional to the input voltages. However, these typical designs can be relatively sensitive to temperature variations. Also, an example of a known single-quadrant multiplier circuit 20 as can be used in a four-quadrant multiplier circuit is shown in FIG. 2.
Thus, a current-mode analog computational circuit addressing the aforementioned problems is desired.